1. Field of the Invention
This invention relates to a color display device for displaying a multicolor image such as letters, figures or the like, and more particularly to a field-sequential color display device constructed by means of a fluorescent display device and color polarizing plates.
2. Description of the Prior Art
There has been proposed a color display device constructed in such a manner as disclosed in Japanese patent application Laying-Open Publication No. 126515/1983. The proposed device is a field-sequential color display device comprising a combination of a fluorescent display device for displaying an image, and color polarizing plates and a liquid crystal shutter for selecting a wavelength of transmitted light.
The conventional color display device proposed is adapted to carry out display of an image according to a field-sequential system rather than a parallel color-mixture system, so that it may improve resolution of the display. However, in order to accomplish full color display of an image, a luminous display device for the conventional color display device is required to exhibit luminous capability over a wide wavelength range. Such requirements will be described hereinafter in connection with a case that a fluorescent display device is used as the luminous display device. In the fluorescent display device, a ZnO:Zn phosphor is used for this purpose because it has the widest wavelength range for luminescence and is excellent in properties such as a useful service life and the like. Although it has an emission spectrum over a substantially whole visible region, it is decreased in luminance in a red region, resulting in a failure in the full color display.
As an approach to such a problem is proposed a fluorescent display device which is constructed so as to arrange a phosphor of a red luminous color adjacent to the ZnO:Zn phosphor, as well as employs a combination of the field-sequential system and parallel color-mixture system. In the fluorescent display device, the ZnO:Zn phosphor is used to obtain display of blue and green luminous colors and the phosphor of a red luminous color is used to obtain display of the color red. Also, a liquid crystal shutter is driven in synchronism with driving of the fluorescent display device, so that color display is carried out in the order of a red display section, a green display section and a blue display section at every line or field. This results in the amount of display of a red luminous color being increased to lead to desired full color display.
A typical phosphor of a red luminous color is, for example, a Y.sub.2 O.sub.2 S:Eu phosphor. Unfortunately, the phosphor has luminous efficiency as low as about 2% of that of the ZnO:Zn phosphor, so that luminance of red luminous display on a color display plane is reduced as compared with blue or green luminous display, resulting in nonuniformity occurring in color display.
In order to improve such nonuniformity, it would be considered to carry out operation for luminous display in the order of the red display section, green display section and blue display section and drive the red display section for a period longer than the blue and green display sections. However, this causes a time used for driving the green and blue display sections to be decreased because a frame cycle is kept constant, resulting in a decrease in overall luminance.